Automatic steering apparatus



L.. A. TRoFlMov 2,453,878

AUTOMATIC STEERING APPARATUS Nov. 16, 1948.

Filed Feb. 5, 1944 2 Sheets-SheeiI l g ov 'o a o o! INVENTOR.

Nov. 16, 1948. A. TRoFlMov AUTOMATIC STEERING APPARATUS 2 Sheets-Sheet 2 V R o Y @,m E T f N ff C Q N Y B Filed Feb. 5, 1944 Patented Nov. 16, 1948 UNITED STATES PATENT OFFICE 2,453,818 i v AUTOMATIC STEERING ArPARA'rUs l Lev A. Trofimov, Willoughby, Ohio Application February 5, 1944, semi No. 521,217

` (cl. 31a-489) Claims.

This invention relates to automatic pilot systems for controlling the course-direction of a vessel, airplane, or other moving dirigible body.

The invention comprises in general a. gyroscope, and a power unit controlled thereby, for moving the course-changing or course-correcting or stabilizing mechanism of the dirigibie body.

As a simple illustrative embodiment of the invention I have chosen to describe it herein as applied to the control of a vessel or airplane rudder, for steering the vessel in two dimensional space; and it is believed that it will then be apparent to those skilled in the art how to apply the invention to the control of the stabilization, direction, and attitude of an airplane, dirigible balloon, or the like in three dimension space; even if more than one such system as that described herein may be needed to effectcomplete control.

Automatic pilot systems of the class referred to havev been proposed, comprising a gyroscope, and a power unit controlled thereby to change the position of the rudder, to hold the vessel on its course, responsive to movements of the vessel or its tendency to move from the course; but in all such prior systems of which I have knowledge, there is unavoidably introduced a time interval or delay between the movement of the vessel fromits course and the correcting movement of the rudder. y

This in some cases is caused by the necessary inclusion in the system of intermediate agencies or operating apparatus between the gyroscope and the power unit, which require time for-their operation; and in other cases is caused by a delay in the response of the power unit itself.

The vessel therefore will have deviated from its course to a great degree before any correcting or course-restoring effect of the system comes into action; and the vessel will swing or yaw from side to side of the course through a wide angle, proportional to the amount of said time interval or delay.

When the dirigible body is of great weight and inertia, the power unit to operate the rudder will accordingly be of great horsepower; and to effect its actuation by the gyroscope the actuating power developed by the gyroscopeV must in general be amplified; and in prior systems this amplifying apparatus has also introduced delay between the actuating movement of the gyroscope and the movement of the rudder.

According to the present invention, this delay has been eliminated or reduced to a negligible minimum. In the specific embodiment of the 2 invention herein disclosed the power unit derives its power from a motor, preferably but not necessarily an electric motor, which at all times runs at full speed or at a high-power speed. A power transmission of the toothed gearing type is provided between the motor and a rotary output shaft operatively connected at all times to the rudder. Some torque is at all times developed by the transmission and applied to the output shaft in opposing directions even while the output shaft is at rest, so that the teeth of the gearing are always loaded and all lost motion in the transmission is eliminated. To cause the output shaft to move in either direction of rotation from rest, or to change the speed or direction of rotation, or to bring it again to rest, all that is necessary is to change -the relative degree of energization of a pair of electromagnetic windings.

These windings are at all times energized. Their energization is balanced or unbalanced as the case may be, byra rheostat or potentiometer operated directly by the gyroscope. The rheostat may be of very small size and respond very sensitively to the gyroscope. l

The rudder accordingly begins to move in one correcting direction or the other instantaneously, upon the initiation of any movement of the vessel from its course, and restores the vessel to its I course, and concurrently restores the rudder to its normal course position.V Furthermore, means is provided by which the rudder will be held in a moved 'position if extraneous influences continue to act on the vessel tending to causeit to leave the course. V

Again, the more rapidly the vessel tends to move from its course, the more rapidly will the' rudder be moved in the corresponding direction and the farther it will be so moved.

Thus `any movement or tendency to movement of the vessel from its course is counteracted instantaneously by a corresponding corrective movement of the rudder.

It is accordingly among the objects of the invention: f

To provide generally an improved automatic pilot system of the class referred to;

To provide an automatic pilot system of the class referred to, in which the objections to prior systems referredto above are eliminated;

To provide an improved automatic pilot system having the advantages and operative characteristics and mode of operation mentioned above;

To provide an automatic pilot system of the class referred to in which the rudder or other entspre steering or stabilizing mechanism ci a dirigible vessel, airplane, or the like, may be moved by the power of a motor, including motors of great horsepower, by changing the relative amounts oi energization ofa pair of stationary electromag netic windings which are at all times'energized, by the movements of the movable element of a potentiometer or rheostat having mechanical connection with a gyroscope.

Other objects will -be apparent to those skilled in the art to which my invention appertains.

My invention is fully disclosed in the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a. diagrammatic view illustrating a system embodying -my invention as applied to the rudder of a vessel;

Fig. 2 is a fragmentary view similar to a part of Fig. l illustrating a modification which in some cases may be used:

Fig. 3 is a diagrammatic view illustrating another embodiment of my invention applicable to -cases in which the power to operate the rudder must be of great horsepower.

.Referring to the drawing. Fig. 1, I havelndicated diagrammatically at I the rudder of a vessel, at 2 the motor supplying power to move the rudder, and at 3 a. gyroscope.

The gyroscope 3 is illustrated diagrammatical- 1y as being of Well known construction, and will be understood without further illustrationy or description; it being believed sufficient to say here that it has arotary element driven by a source of power not shown, and has a shaft 4; and that when the vessel upon which it is mounted is moving along a preselected course, the shaft 4 remains at rest, relative to thevessel and apparatus thereon; but that upon deviation of the vessel from its course in one direction or the other, the shaft 4 will remain rotatively stationary in space; but, relative to the4 vessel,l will be rotated correspondingly in one direction or the other, and upon return of the vessel toward its course will rotate relatively in the opposite direction.

The motor 2 is illustrated diagrammatically as a direct current shunt motor, and runs continuously, tending to run ata constant speed,'so long as the apparatus is in operation. As will be apparent hereinafter, this motor may be any other type or kind of motor, for example an internal combustion motor. Since this motor is not started and stopped in the application of its power to the rudder, but runs continuously, it may run at its most ecient speed and therefore may be of smaller size and with smaller rated horsepower than would otherwise be possible.

Illustrated generally at 5 is a double differential gearing driven by the motor 2. It comprises two spider elements 6 and 'I provided with gear teeth at their outer peripheres meshed together as at 8, and rotated in opposite directions by a gear 9 on the shaft IIJ of the motor 2.

There may be any suitable speed ratio between the motor 2 and the spiders 6 and l, the drawing having been simplified by showing simply one gear 9 between them.

The spider 6 rotatably supports pinions II and I 2 meshed with differential gears I3 and I4; and the spider element 'l rotatably supports pinions I5 and I6 meshed with differential gears il and I8.

Connected to the differential gears I3 and il are pinions I9 and 20 both meshed with a single gear 2| which latter gear is connected t0 an outof the spider elementsv tandfl. s

put shaft 22 upon the end of which is a clutch element 23. The outputshaft 22 may be conksiciered as in two axially aligned parts 22 and 24 which, in the operation of the system, are clutched together by the clutch element 23 and by a clutch element 24 splined for axial movement on the output shaft portion 24.

A cable drumv 23 on the output shaft portion 24 has a. cable 21 wound thereon and passing over pulleys 23 and 23 and connected vat its `ends to opposite arms 30 and 3l on an oscillatably supported rudder post 32 connected to the rudder I.

In a manner to be more fully described, the motor 2 supplies power through the transmission 5 to the output shaft 22-5-24 in' one directionl or the other to move the rudder I in one direction or the other; but if it be desired to' operate the rudder I independently of the automatic pilot mechanism, a change-over to that 'mode of operation may be effected as follows. A lever 33 pivotally supported at 34 is rotated lon its pivot and its inner end, engaged in a clutch shifting groove 33 associated with the clutch element 25, withdraws the clutch element 25 from engagement with the clutch element 23, and the same movement meshes a gear associated with the clutch element 25V with a gear 3I` on 'a shaft 33 to which power is supplied by hand or by motor; the source of such power not-being'shown, to simplify the drawing,y inasmuch as those -skilled in the art will know how to apply such power to the shaft 33.

Connected tothefdiferential gears I4 and I3 are control shafts GI and G2 upon which are mounted the rotary elements of electric generators 39 and 40, which in the preferred type are direct current generators having series field windings 4I and 42 and shunt field windings 43 and 44.

As stated, the spider elements and 1 in this 'I9 and 20 and their differential gears I3 and I1 tendtoremain at rest,.andthe diil'erential gears u and |s and'their nur tsmoff. and G2 tend to rotate in opposite directions at twice the speed The output terminals of thegenerators 39 and 40, driven by the shafts -GI}-andG2 ,'are connectedinseries with each other by acircuit comprising a wire "connecting the, generators to each other, wires 48 and 41 connecting the generators to their respective series'fleld 4I and 42, and a wire 48 connecting the series fields. The generators are poled to oppose each other, potentially.

'I'he shunt field 43 of the generator 39 is connected across that generator, one side of the ileld winding being connected to the wire 46 and the other side being connected through a flexible connector 49 to one end of a' resistor 50, thence through a part of the resistance of the resistor to a movable rheostat arm 5I, and thence by a flexible connector 52 to the wire 45; and the field winding 441s similarly connected across its generator 40, at one end to the wire 4l and at its other end by means of a flexible connector 53 to the other end of the resistor 50 and back to the other side of the generator 40 by way of the arm 5I and the flexible connector 52.

With the rheostat arm 5I in an intermediate position on the resistor 50, the shunt iield windings 43 and 44 will be energized across their respective generators 39 and 40 to a condition of balance at which the potentials, of the generators 2l and 40 will be equal and opposite in the series circuit described above.

Each generator will then generate current in its own local shunt field circuit as described above. This puts a small load or braking action on the shafts GI andv G2 and causes a small torque or load to be developed at the pinions I9 and 20, acting oppositely on the gear 2I, and thereby all lost motion or back-lash is removed from all of the teeth of the interengaged gear teeth of the system.

When the rheostat arm I is in the 4position referred to at which the energization of the two shunt field windings 43 and 44 is balanced, that is, are energized respectively to the degree at which the two generators develop equal load torques, the system is in normal 'balanced condition, and the output shaft 22--24 remains at rest and the rudder I consequently remains at rest.

This condition obtains-when the vessel is proceeding on its course, and the shaft 4 of the gyroscope 3 is relatively at rest. The shaft 4 is connected to the rheostat arm 5I as shown.

If now due to any cause the vessel should deviate or begin to deviate fromits course, in one direction or the other, the gyroscope shaft 4 will begin to turn, relatively, in one direction or the other, and move .the rheostat arm 5| in 4the corresponding direction, to cut resistance into the circuit of one shunt field winding 43 or 44, and cut it out of the other; thereby causing one generator 39 or 40 to have a potential overpowering that of the other, and causing current to flow in the series circuit comprising: the generators, the Series field windings 4| and 42 and the wires 45, 46, 41, and 48 as described.

The generator whose potential is thus made greater than that of the other continues to act as a generator and the current generated by it and flowing from it in the series circuit and through the other, causes the other, to act as a motor. The generatorunit which acts as a generator develops electrical load in the series circuit, which draws more torque from the differential gearing and causes the generator to slow down.

It is a characteristic of this differential gearing as illustrated and described, that no matter at what relative speed the shafts GI and G2 rotate, the ari-thmetical sum of their speeds is a constant. If therefore one of the shafts GI or G2 slows down as just described, the other shaft will be speeded up by the gear interconnections. By causing .the generator unit which is not acting as a generator to motorize, it will be caused to tend to run at a higher speed, by electrical power supplied to it from the one which is running as a generator. By design, as will be understood by those skilled in the art, the speed at which lthe motorizing unit tends to run, may be caused to be at all times greater than the speed at which it tends to be driven by the gearing. It follows that the electrical load developed by the unit which is running as a generator, and which acts as a braking load on the gearing, is not lost, but is conserved and converted by the motorizing unit into mechanical power and put back into the differential gearing system.

By giving the two units 39 and 40 both series and shunt windings, when one unit begins to act as a generator, the electrical load which it develops is rapidly built up or magnified, producing a rapidly magnified braking load on its shaft GI or G2, and this, as will now be clear, causes one shaft GI or G2 to slow down rapidly and run slower than the other.

Upon thus putting braking torque on one shaft GI or G2 and speeding up the other shaft, the torques at the pinions I9 and 20 will no longer be equal and opposite, but will act on lthe gear 2| in the same direction and turn it together with the output -shaft 2I-24, and move the ruddder I.

As a specific illustrative example, if the rheostat arm 5| be moved counter-clockwise, .the generator 40, acting as a generator, will develop more electrical load and torque and put an increased braking action on the shaft G2, which will slow down that shaft and the differential gear I8. This will cause the pinion 20 to increase in speed and to have increased torque applied on it, because the torques on the shaft G2 and pinion 20 are at all times equal. This, in the absence of anyother agency, would cause the gear 2| to turn and to driveI the pinion I9 and cause the shaft GI to increase in speed; but this is supplemented by .the overdriving motor action of the unit 29, which also tends to cause the shaft GI to increase still farther in speed, and causes the pinion I9 to apply torque to the gear 2| .to help drive it.

As the end result, there is a .positionfor the rheostat arm 5I at which the system is balanced, and the gear 2| and output shaft remain at rest; and upon moving the arm 5I by the gyroscope to unbaiance the system, the gear 2| and output .shaft are turned, and al1 of thefpower put into the system by themotor 2 is delivered to the gear 2| to turn it, the turning of the gear 2| resulting from putting a braking load on one of .the shafts GI or G2; and this braking load is converted back into mechanical power and fed back into the gearing system and applied to the gear 2 I.

Inasmuch as the motor 2 i-s constantly running, and the generators 39 and 4I) are constantly driven and the field windings 43-44 are constantly energized, the slightest change in the position of the rheostat arm 5I due to the initiation of deviation of the vessel from its course will cause movement of the rudder in the course-correcting direction. The movement of the rudder in the course-correcting direction will therefore be concurrent with movement of the rheostat arm 5I without the interposition of any time interval therebetween.

When the deviation of the vessel from the course has been slowed down and finally stopped, by movement of the rudder, it is desirable to have the rudder stop moving in the course-correcting direction. To accomplish this the rheostat arm sh'ould then be on the balancing point of the resistor. If the vessel then begins to turn back toward the course, it is desirable to have the rudder reverse and move back toward the normal central position; and to accomplish this the rheostat arm should be on the other side of balancing point, And as th'e vessel approaches the course direction the rudder should move far enough to prevent the vessel from swinging beyond the course-direction and to stop its return movement when in the course-direction.

This is accomplished by the following mean-s taken in connection with the fact that th'e gyroscope shaft stops rotating and reverses when the vessel stops deviating and begins to return.

Upon the output shaft 22 is a cable drum 54 upon which is wound a cable 55 extending in opposite directions from the drum, and running over pulleys 56-55; and the ends of the cable are secured respectively to arms 58-58 connected to a resistor support 59 upon which the resistor 5l is mounted, the support 59 and arms Uil being mounted to rotate in unison about the airis of the shaft il, the diagrammatic drawing showing them` mounted to rotate on the shait as a bearing support. The connection points oi the cable ends to the arms 53 is adjustable to change the elective radial length or the arms d8.

With this arrangement when the arm di moves, say, counter-clockwise to deld unbalancing positions on the resistor td, and the rudder i moves correspondingly in the correcting clockwise direction, rotation oi the shaft 22 which moves the rudder will rotate the drum d, and by means of the cable 5F: will move the resistor support 5S also counter-clockwise, and carry the resistor 5d under the arm 5i so that the balancing point on the resistor moves toward the arm di.

In general as the vessel begins to deviate, the movement of the rheostat arm will at nrst exceed that of the movement of the rudder and resistor support, but this causes the rudder to accelerate and causes the movement of the resistor support to accelerate and overtake the rheostat arm; and this is contributed to by the fact that as the rudder moves it slows down the rate of deviation and correspondingly slows down the relative movement of the gyroscope shaft d, and of the rheostat arm.

The vessel now returns toward the course, and as it does so the rheostat arm is moved to the other side of the balancing position by reversal of the gyroscope shaft 4; and the rudder reverses. Again, the arm gains on the rudder until the latter speeds up and causes the resistor support to overtake the arm, which causes the rudder return to slow down. As the rudder returns it causes the4 vessel to return more and more slowly so that the rh'eostat arm moves more slowly. The rudder and rheotat arm reach their course position at about the same time, but if there should be any overtravel of the vessel from the course it will be corrected by another similar cycle of lesser dimensions.

In Fig. 2 is shown a modification in which the series field windings and 42 have been omitted. the shunt windings 43-44 alone supplying energization to the generators, the `generators being connected in series by the wire 45, and in this case by a wire 48a corresponding to the wire 48 of Fig. 1.

The operation using this modification will be substantially the same as that of the form of Fig, 1 except that when one of the generators begins to generate and drive the other as a motor the electrical load does not build up to as great a value. In other words the system with the modification of Fig. 2 is not quite as sensitive in response as thatof the form of Fig. l, but may in some cases be suficiently sensitive.

In Fig. 3 is illustrated another form of the invention which' may be used when the dirigible body is of great weight and inertia and great horsepower is needed to operate its rudder.

In this connection, it may be stated, as explaining the purpose for the form of Fig. 3, that the form of Fig. 1 could be increased in horsepower size to any extent to adapt it to a dirigible body such as a sea going vessel of great size and inertia, by providing a suiiioiently large rudder l and a sufficiently powerful motor 2, and increasing the size of the differential gearing and the generator units 39 and 40; but this would call for a large rheostat Ell-5l and a correspondingly large gyroscope 3. In some cases, however, it would be more desirable to employ a small horsepower system of. the kind illustrated in Fig. utilizing a small gyroscope, etc., and utilizing the output shaft 22, not to operate the rudder directly, but to actuate a large horsepower system. supplying power to the rudder. Such an arrangement is shown in Fig. 3.

The parts in the upper left hand corner of this figure including the gear d and the output shaft 22 are the same as in Fig. l. The power-supplying motor for this part of this system, however, as shown at 2A, is an alternating current induction motor supplied with current from three phase mains Gli- 60.

The motor for the rudder is shown at Si and is also an alternating current motor of the squirrel cage induction type arranged to be driven continuously from the mains 60. The rudder in this figure is not shown but at 32A is a rudder post from which connection to the rudder is made.

At 5A is a differential gearing and generatormotor arrangement which in its essential parts has been shown as identical with that of Fig. 1, the parts corresponding to those of Fig. 1 having the same reference characters with the sufllx A, by which expedient it is believed that a complete description thereof is unnecessary because it will be understood from the description of the corresponding parts of Fig. l.

Differences and other additional parts, however, will now be described.

The output shaft 22A drives a worm 62 meshed with a worm gear 63 on the rudder post 32A.

In this form the resistor 50A is stationary, that is to say, is not mounted upon a movable resister support as in Fig, 1. A rheostat arm IHA moves over the resistor 50A by being mounted upon a rotatable shaft 64, and the opposite ends of the resistor 50A are connected by wires 65 and 66 respectively to the eld windings 43A and "A, and the arm SIA is connected by a Wire 61 to the wire 45A.

With the mote-r 6i rotating, upon movement of the arm 5IA in one direction or the other over the resistor 50Am the output shaft 22A and consequently the rudder post 32A will be rotated in one direction or the other or brought to rest as will now be clear.

To thus move the rheostat arm 51A in response 'to movements of the gyroscope shaft I, the following means is provided.

At G8 and 69 respectively are a transmitter and a receiver of the Selsyn type comprising three phase stators l0 and 'H respectively and single phase rotors 'I2 and 13 respectively, the stators being interconnected by a three phase system 14l and the rotors being energized across the common single phase alternating current mains 15 which are energized from one of the phases of the three phase mains 60-60.

The rotor 12 is connected to the shaft 22. The rotor 13 is connected to a shaft 16 at one end, the other end of the shaft being connected to the spider element 'I1 of a differential gearing shown generally at 'I8 and comprising pinions 'IS-'I9 rotatably supported by the spider element 'I1 and differential gears 80 and 8l meshed with the pinions. The differential gear is to be driven concurrently with the shaft 22A and to this end is connected to a spur gear 82 which is driven by rotary movement of the pinion 19A. For convenience this driving connection may be made through an idler'gear 83, and at any suitable gear ratio.

The differential gear 8l is connected to the aforesaid shaft 64.

In the operation of the form of Fig. 3, the gyroscope l, responsive to deviation of the vessel from the course, will actuate the differential gearing i and turn its output shaft 22 as described for the form of Fig. 1. This will unbalance the Selsyn units Il and l! and cause rotation of the shaft 16. Rotation of the shaft 1l will turn the spider 11 and cause the pinions 19-18 to react upon the dierential gear I0, which'at this time is stationary and turn the differential gear Il and the shaft Il to move the rheostat arm IIA away from A its balancing position on the resistor IIIA to one side or the other thereof.

This will unbalance the energization of the field windings A and A of the generators 38A and A and cause power of the motor Il to turn the gear 2 IA and thereby the worm l2 and worm gear I3 and the rudder post 32A.

Rotation of the gear IIA, accompanied of course by rotation of the pinion IIA, is transmitted to the gear I2 and rotates the differential gear lll in the direction to reduce or stop rotation of the shaft Il, and movement of the arm IIA, and to ultimately return the arm again to its balancing position.

It is believed that from this brief description of the form of Fig. 3, its operation will be clear; and that it will be apparent that the differential gearing controls the relative positions of the rudder post 32A and rheostat arm 5 IA as does the cable drum 54, cable li, and resistor support 59 of the form of Fig. 1. 'I 'he rudder on the rudder post 32A therefore will be moved to correct for deviations of the vessel from its course in the same way as the rudder I was moved in the form of Fig. 1. l

In practice and for purposes of economy of manufacture, it will be preferable for the units I0 and 40 to be identical, with identical field windings, and for the two parts of the double differential gearing to be alike; and similarly for the units A and 40A and the differential gearings and the field windings of the units of Fig. 3. In such case, for the balanced condition described hereinbefore at which the output shaft 22 or 22A remains at rest, the two field windings would be equally energized. However, the invention may be practiced equally well if the two generator units or their respective field windings are not exactly alike and if the ratios of the gears in the differential gearing is such that the two units do not run at equal speeds, so that in the balanced condition at which the load shaft remains at rest, the fields may be unequally energized.

In order to avoid complications of description and complications in the claims, and to adequately cover the invention by claims, it is believed proper here to use the word balanced as describing the relative degrees of energization of the two respective fields which causes the output shaft to remain at rest, and "unbalanced as describing them whenlthey cause the output shaft to rotate; and these words or their derivatives have been used with this definition in claims.

I claim:

1. An automatic pilot system for dirigible vessels and the like, comprising: a movable element for controlling the direction of the vessel; a continuously running power supplying motor; a transmission for transmitting motor power to the element; the transmission comprising differential gearing constantly driven by the motor; a pair of rotary electro-dynamic devices constantly driven by transmission-transmitted motor power; a rotary output shaft connected to the element;

a pair of continuously energized electromagnetic devices, and a rheostat controlling the degree to which the electromagnetic devices are relatively energized to cause them to be balanced and unbalanced; a gyroscope compass and means associated therewith for causing operation of the rheostat to unbalance the energization of the electromagnetic devices upon deviation of the vessel from its course, and to operate the rheostat toward balancing the devices upon return of the vessel toward its course; the electrodynamic devices being responsive to unbalanced energization of the electromagnetic devices to cause the transmission to deliver power to the output shaft to rotate it and move the element; movable means moved by power delivered by the transmission and associated with the rheostat to operate it to tend to restore balanced energization of the electromagnetlc devices; and the electrodynamic devices being responsive to balanced energization of the electromagnetic devices to cause the transmission to discontinue the delivery of power to the output shaft.

2. The system described in claim 1 and in which the electrodynamic devices have the construction of electric generators and the electromagnetic devices are in the form of field windings for the generators and the generators are driven by the differential gearing; and generate equal electrical loads and develop equal braking loads on the gearing when the energization of their fields is balanced, and develop an increasing braking load on one generator and differential gearing, when the fields are progressively unbalanced.

3. The system described in claim 1 and in which the electrodynamic devices have the construction of electric generators and the electromagnetic devices are in the form of field windings for the generators; and the generators are driven by the differential gearing and generate equal opposing potentials and equal electrical loads when the energization of their fields is balanced; and, when their fields are unbalanced, one is driven as a generator, and drives the other as a motor.

4. An automatic pilot system for dirigible vessels and the like, comprising: a movable controlling element for controlling the direction of the vessel; a continuously running power-supplying motor; a transmission for transmitting motor power to the controlling element; the transmission comprising a rotary output element connected to the controlling element; control means for the transmission comprising a pair of constantly energized electromagnetic windings; the transmission being responsive to deliver power and rotate the output element in one direction or the other or to bring it to rest, as the energization of the windings is relatively unbalanced or balanced respectively; means to control energization of the windings comprising a rheostat, and a gyroscope connected to it to operate it to tend to eiiect unbalanced energization of the windings upon deviation of the vessel from its course, and to tend to eiiect balanced energization of the windings upon return of the vessel toward the course; and means operable by power delivered by the transmission, to operate a rheostat to cause it to tend to restore balance of the windings.

5. An automatic pilot system for dirigible vesselsv and the like, comprising: a movable element for controlling the direction of the vessel; a continuously running power-supplying motor; a transmission for transmitting motor power to the element; the transmission comprising differential gearing constantly iiiven lov the maior; e, pair oi rotary torque developing devices oonstantly driven "oy iransmission-tmnsmitted mo= tor power; a rotary output sheit connected iso the element; torque controiiing means coniroliine the relative torques developed ley the olevioes ibo oeuse them to be balance-d ami unbalanced; e eyrosoope compass and means associated therewith. foiv causing operation of 'elle iomue eontnroiiing means to unloaiance the torolutes upon deviation of the vessel from its course, and to balance iziiem upon return, oi the .vessei toward its course; the transmission being responsive to unbalanced torques to deliver power to the ouipuis shaft to rotate it and move the element; movable ineens moved by powei delivered by the iziensmission and associated with the torque controlling ineens to operate ii to tend to iesioie one ioioiues izo osservo balance; and tine transmission being responsive to balanced iomues to @eue-e the transmission to discontinue the delivery oi power to the output shaft.

mv A. Tooele/mvv.l

(CITED The following; references sire of record in the il@ le of this potent:

UNITED STATES PATENT liiumloei- Nome` Date 942,198 Dey Dec. '1, 1909 il@ 1,818,109 Sperry Aug. 11, 1931 2,113,436 Williams Apr. 5, 1938 2,348,211 Frische et ei. May 9, 1944 2,390,787 Height Dec. 1l, 1945 

